A power converter receives an input voltage and supplies an output voltage to a load (or an electrical device), and the output voltage and corresponding current resulting from the output voltage should meet certain specifications of the load. As an example, the power converter may receive a 12 Volt input voltage, and the load may require a 1.5 Volt output voltage to operate properly, which can be referred to as a target voltage.
In such an example, the power converter converts the 12 Volt input voltage to the 1.5 Volt output voltage, and supplies the 1.5 Volt output voltage to the load. In converting the input voltage to the output voltage, the power converter regulates the output current and voltage that is being supplied to the load such that 1.5 Volt is supplied to the load.
Typically, the power converter controller comprises switching logic that turns on and off, often referred to as a duty cycle, in order to regulate the output voltage and output current. The switching logic is designed to ensure that the output voltage remains within a specified range. In this regard, the output voltage may vary slightly above (overshoot) or slightly below (undershoot) the target output voltage for the load, especially under dynamic transients.
In order to ensure that the output voltage remains within a desired range of the target output voltage with minimum deviation under dynamic transients and other variations, e.g., 1.5 Volts as described in the example, power converters often have a closed-loop controller that measures the difference between the output voltage and a reference voltage. Based upon the measurement, the controller may modify the duty cycle of the switching logic in order to increase and/or decrease the duty cycle to keep the output voltage within a desired range of the target output voltage.
The controller design and related transfer function for the closed loop compensation may become very complicated and time and resources consuming. They also may require significant circuitry size that consumes a significant amount of power to perform estimation and complex calculations. They are often designed based upon approximating the power stage transfer function of the power converter. It is often difficult to obtain a design with the best performance that operates under desired constraints. In addition, the controllers are often designed based upon criteria such as gain margin and phase margin. Such criterion does not guarantee that the controller will achieve the optimum dynamic output voltage deviation and settling time (closed loop performance) after a load transient, increase or decrease, or under other operation variations such as input voltage variations. Furthermore, the power converter closed loop performance may be affected by aging, temperature variations, manufacturing process variations, and other parameters such as output and input capacitance, inductance, and switching frequency that can affect the power stage transfer function of the power converter and affect the closed loop performance and stability of the closed loop converter system. In this case, a different closed loop compensator design may be needed to maintain and get back the good closed loop performance and stability.